Adding shape-selective zeolites such as ZSM-5 to cracking catalysts, e.g. those used in fluidized catalytic cracking (FCC), improves the octane rating of the gasoline boiling range product. But adding these shape-selective zeolites to the FCC process increases light olefins production, particularly the yield of n-butenes. The n-butenes are not, of themselves, a particularly marketable product, and it would be beneficial to upgrade these normal olefins.
Butene exists in four isomers: butene-1, cis-butene-2, its stereo-isomer trans-butene-2, and isobutene. Conversions between the butenes-2 is known as geometric isomerization, whereas that between butene-1 and the butenes-2 is known as position isomerization, double-bond migration, or hydrogen-shift isomerization. The aforementioned three isomers are not branched and are known collectively as normal or n-butenes. Conversion of the n-butenes to isobutene, which is a branched isomer, is widely known as skeletal isomerization.
U.S. Pat. No. 4,581,474 to Hutson, Jr., et al. teaches a combination alkylation-etherification process in which unreacted C.sub.4 olefins produced by etherification are contacted with molecular sieves to absorb 2-butenes and the remaining 1-butenes are split so that a first portion is subjected to double bond isomerization and a second portion is subjected to skeletal isomerization to form isobutene for etherification.
U.S. Pat. No. 4,684,757 to Avidan teaches a method for converting an alcohol feed to an etherate and an isoparaffinic alkylate useful as a gasoline blending stocks.
U.S. Pat. No. 4,891,466 to Chou et al. teaches an integrated process which first isomerizes the feed olefin double bonds and then alkylates the isomerized product in the presence of a supported Lewis acid.
U.S. Pat. No. 5,001,292 to Harandi teaches an integrated etherification/oligomerization process for upgrading oxygenates, light olefins, and paraffins to higher molecular weight gasoline blending components.
U.S. Pat. No. 5,013,329 to Bell et al. teaches a process which etherifies n-olefins and i-olefins in sequential reaction zones and then oligomerizes the unreacted light olefins to form useful gasoline components.
U.S. Pat. No. 5,091,590 to Harandi et al. teaches an integrated process for upgrading an olefin feedstock containing a mixture of iso-olefin and linear olefin to produce tertiary-alkyl ether and gasoline components comprising dimerized iso-olefin.
U.S. Pat. No. 5,100,533 to Le et al. teaches a process for upgrading a fresh virgin naphtha by cracking, etherifying the resulting C.sub.5 -olefins, recovering the etherate, and oligomerizing the unreacted olefins.
U.S. Pat. No. 5,106,389 to Harandi et al. teaches a process for producing alkyl tertiary alkyl ethers and alkylated aromatics useful as high octane gasoline blending stocks.
U.S. Pat. No. 5,258,569 to Chu et al., incorporated herein by reference, teaches alkylation of isoparaffin with olefin in the presence of MCM-36 as catalyst to provide alkylate.